1. Field of the Invention
This invention relates generally to vehicle transmissions and more particularly a control system associated with an automatic transmission clutch mechanism which reduces engine drag when a vehicle is idling.
2. Brief Description of the Prior Art
In many vehicles with automatic transmissions, a fluid coupling, torque converter or hydrodynamic clutch was driven by the engine crankshaft. When the vehicle was not in motion and the engine idling, the engine was still driving the torque converter, fluid coupling or hydrodynamic clutch and thus expending energy to overcome the flow resistance caused by a stationary transmission output shaft. As a result, fuel was unnecessarily consumed and exhaust emissions generated especially in city driving.
In published German Pat. DE-OS No. 2 545 798, a control device which provided reduced fuel consumption and minimized exhaust emissions was disclosed. Among the problems which may have been encountered when a clutch was utilized for the purpose of disengaging an engine from a transmission at idle speeds was that shifting shocks were readily generated during acceleration especially when the accelerator was depressed rapidly and the clutch was engaged at high engine torque and engine speed.
Another problem which was encountered in conjunction with the employment of clutch mechanisms in automatic transmissions was that it was undesirable and often dangerous for a clutch to disengage at rapid vehicle speed since the engine and transmission would not be available to assist in vehicle braking.